Option for Cascade Delete for References or On Delete

Question

In Rails 4.2, when creating a table or adding a reference via references or add_reference how do you specify that the foreign key should cascade on delete.

Command to generate scaffold:

rails g scaffold Child parent:references name:string

Resulting migration:

create_table :childs do |t|
  t.references :parent, index: true, foreign_key: true
  t.string :name

  t.timestamps null: false
end

Answer 1

This should work

create_table :childs do |t|
  t.references :parent, index: true, foreign_key: {on_delete: :cascade}
  t.string :name

  t.timestamps null: false
end

According to ActiveRecord::ConnectionAdapters::TableDefinition#references, if a hash is specified on the foreign_key option, it is directly passed down into the foreign_key method.

source:

foreign_key(col.to_s.pluralize, foreign_key_options.is_a?(Hash) ? foreign_key_options : {}) if foreign_key_options

Answer 2

Also note that if you already have the table setup, you can generate a migration to update the foreign_key by doing the following:

  def up
    remove_foreign_key :children, :parent
    add_foreign_key :children, :parent, on_delete: :cascade
  end

  def down
    remove_foreign_key :children, :parent
    add_foreign_key :children, :parent
  end